The present invention pertains generally to assembly systems, particularly of the type including conveyors defining a path of travel for transporting a workpiece between workstations, and more particularly the present invention pertains to an overhead conveyor system.
In automotive production lines, it is generally known to transport individual workpieces, such as automotive body panels, frame components, etc., to and between workstations where selected operations, such as welding, are performed by workers, robots, or other processing equipment. Transporting individual workpieces to, and accurately placing the workpieces at, a desired workstation on a production line poses numerous difficulties. Tooling and other processing equipment at a workstation create obstacles to be avoided by the incoming and departing workpieces. After reaching any given workstation, the workpieces need to be accurately positioned within the workstation so that the necessary processing operations can be performed. The efficiency considerations of modern production lines and the like demand that workpiece delivery to a workstation be as rapid as possible.
In many common production lines and other assembly applications, workpieces are transported along an overhead rail, for instance a monorail. Motor-driven trolleys travel along the rail to and between various workstations. Electrical conductors can be provided along the rail to provide power to the trolley motors mounted on each carriage. The carriages carry workpieces along the path defined by the rail for delivering the workpieces to the various workstations.
Prior known conveyor systems typically use an electrified monorail system (EMS) with intelligent carriers. Performance characteristics of this type of electrified monorail system with one wheel drive typically vary inversely with respect to mass and speed. As the mass to be conveyed increases, typically the speed of transfer decreases. A typical electrified monorail system configuration provides a transfer cycle time for 24 feet of movement in 9.5 seconds, carrier stopping accuracy within plus or minus 2.0 millimeters, and a carrier capacity of up to 2000 lbs. The electrified monorail systems include an electrified rail with bus bars and intelligent carriers with on board microprocessors. Overhead carrier positioning is accomplished with switches and an overhead carrier control box. This type of system requires alignment between adjacent portions of the rail and adjacent portions of the electrical bus bars. Durability of the electrified monorail system is dependant on the life of the electrical brushes or contacts, wear of the electrical bus at connections, and wear of the carrier trolley wheels. Off center loads require side guide rollers and hanger assembly for the carriers of an electrified monorail systems. Each carrier has an on board processor. The carrier positioning switches are typically overhead mounted and zone cuts or controls are predetermined and not easily modified. The length of an electrified monorail system is typically enlarged due to the requirement of enter and exit stations adjacent to any curves in the transport line. A workstation width is typically less than 50 feet while station height is approximately 16xc2xd feet. Each carriage typically includes single roller braking. Carrier positioning switches are typically located in overhead locations. New model carrier set up on an electrified monorail system requires additional carriers with controls and a carrier insert/removal facility. Coordination is required between the carrier trolley (i.e. facility source) and the carrier with antler (i.e. tooling source). All carriers require programming for each intelligent carrier being replaced with the new model setup.
It would be desirable in the present invention to provide an overhead conveyor system that would overcome the deficiencies of the previously known electrified monorail system. The present invention includes a high speed overhead power roll system. The high speed overhead power roll system provides transfer cycle time for 24 feet of movement in approximately 6.5 seconds. The carrier stopping accuracy with the versaroll overhead monorail system is plus or minus 1.5 millimeters. The load carrying capacity of the carrier of the versaroll overhead monorail system is 3000 lbs. The overhead conveyor system according to the present invention includes overhead power rollers and are connected with belts for transferring rotary motion along connected segments of adjacent rollers. According to the present invention, the carrier is provided without controls mounted on the carrier. However, a passive radio frequency tag could be provided on the carrier if desired without requiring power input through the carrier. Along aligned linear segments of the path of travel of each carrier, the power rolls are aligned with one another and interconnected with belts for driving the interconnected rollers with a single motor. Preferably, each motor located at a workstation along the path of travel is a variable frequency reversible drive or servo drive, while return loops can use standard electric drives with starters. A support member for each carrier operably engages with the complementary rollers to provide built-in compliance. In the preferred embodiment, a round support member or pipe operably engages with complementary round concave surfaces formed on the rollers. The present invention provides multiple wheel engagement when accelerating and/or decelerating. The present invention eliminates exposed electrical contacts as required in the prior known electrified monorail system. The carrier requires no on board power or processor systems, since the carrier latch can be checked externally prior to leaving any workstation. All variable frequency drives are mounted with corresponding control panels at associated workstations. The present invention combines entrance and exit stations of each curve into a single turntable with high speed rotary table permitting shortening of the overall line length by approximately 2 turning radiuses. The estimated height of each station, according to the present invention is approximately 16 feet, since no clearance is required for carrying a motor on the top of each carrier. The only electrical component with limited accessibility according to the present invention are the power roll motors which are mounted on the overhead rail system and the belts extending between adjacent power rollers. All carrier positioning switches are located at the floor level for easy accessibility and maintenance. Fewer components according to the present invention require safety wiring. The carrier assembly according to the present invention is a single welded carrier unit. New model carrier setup requires additional carriers and associated workstation controls, and a carrier insert/removal facility. Each carrier can be validated at the tool shop. Simple logic setup can be provided to manipulate multiple model selectivity lines with table indexing. Simple welded construction carriers can be provided so that robot utilization can be increased as a result of the faster transfer rate of approximately 6.5 seconds for 24 feet.
An overhead conveyor system according to the present invention provides a plurality of rollers rotatably mounted in fixed locations spaced along a path of travel. At least one motor drives at least a portion of the plurality of rollers in rotation through a series of interconnected belts extending between adjacent rollers along at least a predetermined segment of the path of travel. At least one carriage is supported on the rollers for movement along the path of travel in response to rotation of the rollers. Each carrier has at least one elongate member continuously engagable with at least two rollers simultaneously while the carriage moves along the path of travel. Each roller is operably connected to a common shaft with a first pulley and a second pulley. A plurality of belts are engaged between adjacent rollers connecting the first or second pulley of one roller with the corresponding first or second pulley of an adjacent roller for transmitting rotation from a single motor to the plurality of rollers along the segment of the path of travel.
Other applications of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the invention is read in conjunction with the accompanying drawings.